[Cosmo-media] mirror matter and the Hubble constant - Cyr-Racine et al

[Boud Roukema]

Dzień dobry, [cc cosmo-media mailing list]

Napiszę po angielsku, ale możemy zmienić między językami jak będzie potrzebny.

Apparently you are interested in the article Cyr-Racine et al 2022:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.201301.

The article presents a rather speculative, but interesting, hypothesis
about mirror matter, offering a possible explanation of the Hubble constant puzzle.

The article starts with a mathematical rescaling aimed at
understanding the relation between the standard cosmological and
observations, and proposes that this purely mathematical exercise could have a
physical interpretation in terms of mirror matter.

The first paragraph on page 201301-3 gives a brief description of "mirror matter",
and how (if it exists) it would relate to ordinary matter.

Figure 1 shows that the authors' mirror matter model would be consistent with
the statistics of Planck observations of the cosmic microwave background.

Figure 2 shows that the model could provide a high value of the Hubble constant,
of about 73 km/s/Mpc, and what the values of other parameters would have to be
for the model to be observationally viable.

* Figure 2 bottom-left and bottom-right show values of parameters of the model
that are most likely not observable.

* Figure 2 top-right shows the value of the helium abundance Y_p that
would be required, and the text (left-hand column of page 201301-4)
gives the numbers involved. The helium abundance is
well-constrained observationally, and the text acknowledges that a bit more
speculation regarding properties of the model is needed in order for
the model to become observationally viable - this is discussed more on page
201301-4. In other words, the model does not quite work, and the authors
suggest future calculations that might help.


Personally, I find a more likely explanation of the Hubble constant
puzzle to be much simpler, related to the fact that the Universe is
inhomogeneous.  In terms of real observations, the local part of the
Universe that we observe is necessarily smaller than more distant
parts of the Universe; as a first approximation, this is a simple geometric
effect. Deviations from the average are generally higher in smaller spatial
regions. Our observations (made within our lifetime) necessarily come from
light that passes through our local Universe - which is not quite the
same as an "average" part of the Universe. So deviations on small
scales are not so surprising. The difficulty is doing the modelling
correctly, which is an ongoing research task.

You could look at these some of the following articles by our
cosmology group for more details of this class of explanations for
dark energy and for the Hubble constant puzzle, although this work is
still research in progress:

* https://ui.adsabs.harvard.edu/abs/2013JCAP...10..043R
* https://ui.adsabs.harvard.edu/abs/2013IJMPD..2241018R
* https://ui.adsabs.harvard.edu/abs/2015CQGra..32u5021B
* https://ui.adsabs.harvard.edu/abs/2016IJMPD..2530007B

Cheers
Boud